Apparatus for compressing chipboards

ABSTRACT

Improved apparatus for the production of chipboard wherein the gap width between two heated pressing members at the commencement of the pressing operation is smaller than the thickness of the chipboard to be manufactured.

United States Patent 1191 Ettel 1451 Aug. 27, 1974 54 APPARATUS FORCOMPRESSTNG 3,278,659 10/1966 Willy 425/224 x I v 3,309,444 3/1967Schueler 264/122 X CHIPBO S 3,391,233 7/1968 Polovtseff 425/373 xInventor: Hubert EH91, Telchhute, rm y 3,632,734 1/1972 Haygreen 264/122Assignee Wilhelm Maude 3,734,669 5/1973 Ettel 425/373 [22] Filed: May1972 Primary ExaminerJ. Spencer Overholser [21] Appl.'No.: 256,108Assistant ExaminerJohn E. Roethel A Attorney, Agent, or FirmMo1inare,Allegretti, Newitt 30 Foreign Application Priority Data wtcoff May 29,1971 Germany 2126935 57 ABSTRACT [52] US. Cl 425/373, 264/109, 425/224 1[51] Int. Cl B29j 5/08, B30b 5/04 Improved apparatus for the productionof chipboard [58] Field of Search 264/ 109, 112, 122; wherein the gapwidth between two heated pressing 425/224, 335, 373 members at thecommencement of the pressing operai tion is smaller than the thicknessof the chipboard to [56] References Cited be manufactured. 2 UNITEDSTATES PATENTS v 3,216,059 11/1965 Voelskow 425/336 x 3 m 1 Drawing fBACKGROUND OF THE INVENTION The invention relates to an apparatus forproducing chipboard, in which a layer or bed of wood chips, to whichbinders are added, is scattered onto a steel band and the chips movedinto a gap between two heated pressing components which compress thewood chip layer to produce the chipboard.

In the prior known apparatus for compressing chipboards, wood chips withadded binders are scattered on a steel band, which is moved into a gapbetween two heated pressure plates. The pressure plates are then movedtowards one another and compress the wood chips until a mutual spacingis produced. This spacing is determined by spacer elements between thepressure plates. Since the layer of wood chips settles during thepressing operation, its' resistance to the pressing dies is reduced, andas a result, the compressing pressure can be reduced as the pressingtime increases. With these known apparatus for compressing woodchipboards, at no instant is there affected a compression of the layerof wood chips to a dimension which is smaller than the thickness of thechipboard which is to be manufactured. Since the spacer element alwaysguarantee a constant spacing, the layer or bed of the'wood chips is heldduring the pressing operation at a constant thickness, until the curingof the binder has occurred. In this way, there is no springing back, orat most, only a very slight springing back, depending on'the elasticproperties of the manufactured and cured chipboard.

In order to produce smooth surfaces which, as far as possible, are freefrom pores, it is known to first spread or scatter a layer of fine woodchips, which are to form the lower external surface. A usually thickerlayer, which is to form the middle layer of the chipboard to bemanufactured is then added to be followed by a top layer of fine chipswhich forms a smooth upper surface layer. The use of very fine chipsdid, however, present difficulties in connection with the mixing of thefine chips with binders, which requires a device'for scattering that issubstantially more complicated. Furthermore, fine wood chips do notcontribute to or increase in strength in the board, particularly withrespect to bending strength.

SUMMARY OF THE INVENTION An'object of this invention is to provide asimple arrangement for compressing chipboards, whereby it is possible toproduce a smoother surface than with the previously known chipboardsand, as far as possible, to

- have a greater strength.

This object which forms the basis of this invention, is achieved bymaintaining the width of the gap between the two pressing components atthe commencement of the pressing operation at a distance smaller thanthe thickness of the chipboard to be manufactured.

It was found that by an initial, brief, increased compression of thechip layer to a. dimension smaller than the intended final thickness ofthe chipboard to be manufactured, an extremely strong compression of thechips is produced. This leads to a very rapid penetration of the heatfrom the pressing dies or pressing cylinders into the outer zones of thecompressed layer or bed of chips, particularly when using a continuouslyoperating arrangement. As a consequence, the outside layer is curedparticularly quickly and is given the strength required of it. Moreover,by the high degree of compression, a substantially greater freedom frompores is produced. This leads to a better surface quality.

Since the increased compression to a smaller or undersized dimensiontakes place for only a short period of time with the apparatus of thisinvention, the inner portion of the chipboard will spring outwardlyagain, since curing in this portion has still not occurred. The extentthe inner portion springs out is determined by the continuing downstreamcompressive pressure or the width of the following pressure gap, whenusing a 'continuously operating arrangement, and by the thickness of theheaped layer of chips and the material properties of the chips. Theoutward springing produces a smaller chip density in the central regionof the board, where, as is known, the chips only contribute to a smalldegree to the strength of the chipboard. By means of the simpleconstruction of this invention, especially a continuously operatingarrangement for the manufacture of chipboards, it is possible to producea board having high surface quality, high strength, and a lowconsumption of material which results in a lower 1 weight.

With an apparatus for continuously manufacturing chipboards, theteaching of this invention can be achieved in a quite simple manner byadjusting the gap between two pressure cylinders to a distance smallerthan the thickness of the chipboard which is to be manufactured.Following the pressing gap, the'pressure cylinder is wrapped or embracedby a steel band under tension, at a spaced apart distance correspondingto the thickness of the chipboard to be manufactured.

The pressure'cylinders can be mounted for movement relative to oneanother and can be pressed against one another in such a way that therequired narrowing or undersize of the pressure gap is produced at thestart of the pressing operation. By pretensioning the pressure cylindersrelative to one another at a certain force, heat expansions of theheated pressure cylinders scarcely have any effect.

The pressing cylinders can also be fixedly mounted,

however, it is expedient for at least one pressing cylin-- DETAILEDDESCRIPTION OF THE INVENTION AND DRAWING The invention is hereinafter tobe more fully ex plained by reference to a constructional example shownin the drawing. Chips 2, to which a binder is added, are scattered bymeans of a scattering or broadcasting machine 1, on a band 3, which runscontinuously in the direction of arrow 4 over a table 5. In this way, aconstant layer or bed 6 of chips is formed.

This bed of chips travels on the band 3, which is preferably made ofsteel, into a gap 7 formed between a large heated pressure cylinder 8and a small heated pressure cylinder 9. The band 3 wraps around themajor part of the pressure cylinder 8 following the gap 7 and then runsaround a guide roller 10. In the wrapping region of the pressurecylinder 8, a gap 11 is formed between the cylinder and the band 3. Thisgap is filled by the compressed wood chips or, strictly speaking, thealready partially cured chipboard.

The width of the gap 7 between the pressure cylinders 8 and 9 is smallerthan the thickness of the chipboard which is to be manufactured. Forexample, the width of gap 7 is 3.8 mm when the thickness of thechipboard to be manufactured is 4.2 mm. In turn, the width of the gap 11is approximately the same as the thickness of the chipboard to bemanufactured, i.e., about 4.2 mm.

By the excessive compression in the narrowed gap 7, a particularlyintimate thermal contact is produced between the surface of band 3 whichrests on the heated pressure cylinder 9, the adjacent region of thelayer 6, the surface of the heated pressure cylinder 8 and the oppositesurface region of layer 6. This produces a rapid curing of the binder inthe chips. Preferably the curing in the region of the gap 7 occurs in atleast the surface regions. This curing takes place with a high degree ofcompression in the gap 7, so that a high density is guaranteed in thesurface region of the chipboard to be manufactured.

After leaving the gap 7, the'partially cured chipboard springs out againin the middle region of the board. This is because no curing or only aslight curing has occurred, and as a result, the middle region of thechipboard is no longer as strongly compressed. As a result, in regardsto strength, the chipboard has a lower density in the less significantcentral region. Hence, wood is saved and a lower weight is produced. Thecuring of the central region of the chipboard then occurs in the gap 11between the band 3 and the pressing cylinder 8. To "produce a uniformtemperature transversely of the chipboard in the region of the gap 11,it may be expedient to additionally heat the band 3 in the wrappingregion of the pressing cylinder 8.

In the example as shown, the pressing cylinder 9 is provided withbearings 12,- which are displaceably mounted on a guide 13 substantiallyin the direction towards the pressing cylinder 8. In this way, the gap 7between the pressure cylinders 8 and 9 is readily adjustable. Theadjustment of gap 7 can be made by appropriate establishment of acertain pressure on the bearing 12 in the direction of the pressurecylinder 8. The width of the gap 7 also depends on the thickness of thelayer 6. Layer 6, however, can very easily be kept constant, so that aconstant width in the gap 7 is produced.

It is also possible to move the bearings 12 by a con trol mechanism, isnot shown. This movement depends on the width of the gap 11 and thus onthe thickness of the chipboard to be manufactured.

I claim as my invention:

1. In an apparatus for producing chipboard from a layer of wood chipsand binders, said chipboard having a predetermined thickness, saidapparatus including a first and second heated pressure member and asteel band, said steel band carrying said layer between said first andsecond heated pressure members, the improvement comprising means forproducing high chip density outer regions and a low chip densityintermediate region in said chipboard, said producing means includingmeans for positioning said first heated pressure member relative to saidsecond heated pressure member to initially compress said layer to athickness less than said predetermined thickness.

2. An improvement as claimed in claim 1 wherein said first heatedpressure member is a first pressure cylinder and'said second heatedpressure member is a second pressure cylinder, said first and secondpressure cylinders defining a gap therebetween, said gap being less thansaid predetermined thickness.

3'. An improvement as claimed in claim 2 wherein said steel band wrapsaround a portion of said first pressure cylinder to define a second gapbetween said steel band and said portion of said second pressurecylinder and downstream from said gap between said first and secondpressure cylinders, said second gap being substantially equal to saidpredetermined thickness.

1. In an apparatus for producing chipboard from a layer of wood chipsand binders, said chipboard having a predetermined thickness, saidapparatus including a first and second heated pressure member and asteel band, said steel band carrying said layer between said first andsecond heated pressure members, the improvement comprising means forproducing high chip density outer regions and a low chip densityintermediate region in said chipboard, said producing means includingmeans for positioning said first heated pressure member relative to saidsecond heated pressure member to initially compress said layer to athickness less than said predetermined thickness.
 2. An improvement asclaimed in claim 1 wherein said first heated pressure member is a firstpressure cylinder and said second heated pressure member is a secondpressure cylinder, said first and second pressure cylinders defining agap therebetween, said gap being less than said predetermined thickness.3. An improvement as claimed in claim 2 wherein said steel band wrapsaround a portion of said first pressure cylinder to define a second gapbetween said steel band and said portion of said second pressurecylinder and downstream from said gap between said first and secondpressure cylinders, said second gap being substantially equal to saidpredetermined thickness.